This invention relates to new photo-crosslinkable liquid crystalline compounds, liquid crystalline mixtures which contain such compounds, and their use in the cross-linked condition as optical components.
Photo cross-linkable liquid crystals, which are provided with an appropriate amount of a photoinitiator, can be oriented on a substrate or in a cell by suitable orienting layers or in a field and then in this state can be cross-linked by irradiation with light of a suitable wavelength. The liquid crystal orientation in the structure thus produced is maintained, even at high temperatures. Optical components, such as waveguides, optical grids, filters and retarders, piezoelectric cells and cells with non-linear optical (NLO) properties etc. may therefore be produced using this procedure. Such optical elements may be used, for example, for frequency doubling (SHG) or in colour filters.
The optical properties of the liquid crystal materials used in the manufacture of the aforementioned optical components such as birefringence, refractive indices, transparency, etc. are selected according to the field of application in which they are to be used. Thus materials for optical filters, for example, must exhibit a high birefringence xcex94n at low dispersion n=f(xcex).
In addition to the use of photo-crosslinkable liquid crystals in the manufacture of optical components, such liquid crystalline materials are also suitable as glass fibre cladding for optical data transmission. Photo-crosslinkable liquid crystals exhibit anisotropic thermal conductivity, enabling heat to flow in certain directions. The use of such materials reduces the thermal coefficients of expansion and reduces microdistortion losses. This results in increased mechanical stability.
Liquid crystal media used in the manufacture of optical components are generally used in the form of liquid crystal mixtures. It is desirable that liquid crystal components are chemically and thermally stable, readily soluble in conventional solvents, and stable to electrical fields and electromagnetic radiation. They should have a suitable mesophase in the temperature range of from approx. 25xc2x0 to approx. +100xc2x0 C., particularly from approx. 25xc2x0 C. to approx. +80xc2x0 C. Moreover, since liquid crystals are usually used as mixtures of several components, it is important for the components to be well miscible with one another.
Conventional photochemically oligomerisable or polymerisable liquid crystals generally have a high melting and clearing point. The disadvantage of this is that spontaneous, thermal polymerisation may occur prematurely during processing, this polymerisation occurring at temperatures just below the clearing point where the viscosity is low and therefore favourable for a good orientability. This spontaneous polymerisation represents a significant problem as it results in the formation of domains, which substantially impairs the optical and thermal properties in the crosslinked layers produced. In an attempt to overcome this problem, complicated liquid crystal mixtures having several components have been used. Although the lower melting and clarifying points of these mixtures means that they can be processed at lower temperatures it presents the risk of crystallisation of the liquid crystal components.
There is, therefore, a need for photochemically oligomerisable or polymerisable compounds exhibiting relatively lower melting and higher clearing points. Such compounds can be satisfactorily processed in the liquid crystalline condition at temperatures above room temperature, and also in solution. These compounds find particular application in the manufacture of optical components. There is also a need for compounds that can be readily orientated and structured without the formation of domains, and which also exhibit excellent thermal and long-term stability in the crosslinked condition. There is also a need for liquid crystal mixtures with an adjustable optical anisotropy. Liquid crystal mixtures having an adjustable anisotropy are considered to be particularly suitable for the manufacture of optical retarders, for example, in which the optical retardation may be adjusted.
Conventional photochemically oligomerisable or polymerisable liquid crystals, such as those described in EP-A-0 331 233, ACS Symp. Ser. (1996)), 632, 182-189 and in Chem. Mater. (1996), 8 (10), 2451-2460, for example, consist mainly of aromatic rings, and therefore generally exhibit a very high optical anisotropy.
The present invention seeks to address at least some of these problems. A first aspect of the present invention provides compounds with the general formula I:
Rxe2x80x94S1xe2x80x94Axe2x80x94Z1xe2x80x94Bxe2x80x94S2xe2x80x94Rxe2x80x83xe2x80x83I
where
A and B are independent ring systems with the formulae a1, a2 or b, 
wherein, in teh trans-1,4-cyclohexylene ring, one or two non-adjacent CH2 groups may be replaced by oxygen, and whereby, in the 1,4-phenylene ring, one or two non-adjacent CH groups may be replaced by nitrogen;
L1, L2, L3 represent, independently, hydrogen, C1-C20-alkyl, C1-C20-alkenyl, C1-C20-alkoxy, C1-C20-alkyoxycarbonyl, formyl, C1-C20-alkylcarbonyl, C1-C20-alkylcarbonyloxy, halogen, cyano or nitro;
Z1, Z2, Z3 represent, independently, a single bond, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OOCxe2x80x94, xe2x80x94(CH2)4xe2x80x94, xe2x80x94O(CH2)3xe2x80x94, xe2x80x94(CH2)3Oxe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94;
S1, S2 represent, independently, a spacer unit, such as a straight chain or branched alkylene grouping xe2x80x94(CH2)r, substituted if necessary singly or multiply with, for example, fluorine, or xe2x80x94((CH2)2xe2x80x94O)rxe2x80x94, or a chain with the formula xe2x80x94(CH2)rxe2x80x94Yxe2x80x94(CH2)sxe2x80x94, where Y represents a single bond or a linking functional group such as xe2x80x94Oxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OOCxe2x80x94, xe2x80x94NR1xe2x80x94, NR1xe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94NR1xe2x80x94, xe2x80x94NR1xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94NR1xe2x80x94, xe2x80x94NR1xe2x80x94COxe2x80x94NR1xe2x80x94, xe2x80x94Oxe2x80x94OCxe2x80x94Oxe2x80x94, xe2x80x94CHxe2x89xa1CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94; where R1 represents hydrogen or low alkyl, and where r and s each represent a whole number from 0 to 20 on condition that 2xe2x89xa6(r+s)xe2x89xa620;
R represents crosslinkable groups with the structure CH2xe2x95x90CHxe2x80x94, CH2xe2x95x90CHxe2x80x94COOxe2x80x94, CH2xe2x95x90C(CH3)xe2x80x94COOxe2x80x94, CH2xe2x95x90C(Cl)xe2x80x94COOxe2x80x94, CH2xe2x95x90C(Ph)xe2x80x94COOxe2x80x94, CH2xe2x95x90CHxe2x80x94COOxe2x80x94Phxe2x80x94, CH2xe2x95x90CHxe2x80x94COxe2x80x94NHxe2x80x94, CH2xe2x95x90C(CH3)xe2x80x94CONHxe2x80x94, CH2xe2x95x90C(Cl)xe2x80x94CONHxe2x80x94, CH2xe2x95x90C(Ph)xe2x80x94CONHxe2x80x94, CH2xe2x95x90C(COORxe2x80x2)xe2x80x94CH2xe2x80x94COOxe2x80x94, CH2xe2x95x90CHxe2x80x94Oxe2x80x94, CH2xe2x95x90CHxe2x80x94OOCxe2x80x94, Phxe2x80x94CHxe2x95x90CHxe2x80x94, CH3xe2x80x94C(xe2x95x90NRxe2x80x2)xe2x80x94, cis- or trans-HOOCxe2x80x94Rxe2x80x2xe2x95x90CRxe2x80x2xe2x80x94COOxe2x80x94, 
Ph represents a phenyl group,
Rxe2x80x2 represents methyl, ethyl, propyl, butyl or pentyl;
Rxe2x80x3 represents methyl, methoxy, cyano or halogen,
with the proviso that at least one of the ring systems A or B represents a ring system with the formula a1 or a2, Z1 and/or Z2 represents a single bond, and xe2x80x94Rxe2x80x94S1 and Rxe2x80x94S2 do not contain xe2x80x94Oxe2x80x94Oxe2x80x94 or xe2x80x94Nxe2x80x94Oxe2x80x94 groups.
Compounds containing a structural unit with the formulae a1 or a2 in the molecule 
(that is to say, a structural unit with the above-mentioned formulae a1 and a2 and in which Z2 represents a single bond) have been found to exhibit relatively high clearing points and can be processed at room temperature, preferably as components of liquid crystal mixtures. It is also possible to orientate and structure the compounds or mixtures thereof without the formation of domains. As a component of a LC mixture, they are able to improve the orientability of the liquid crystal mixture on orientation layers thereby improving the contrast of optical display devices. In addition they exhibit extremely good thermal and long-term stability.
By the expression C1-C20-alkyl, C1-C20-alkoxy, C1-C20-alkoxycarbonyl, C1-C20-alkylcarbonyl, C1-C20-alkylcarbonyloxy it should be understood to mean, in the context of this invention, straight or branched chain saturated hydrocarbon residues, with up to 20 carbon atoms, e.g. methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, methoxy, ethoxy, n-propoxy, i-propoxy, butoxy, pentyloxy, hexyloxy, heptyloxy, octyloxy, nonyloxy, decyloxy, undecyloxy, dodecyloxy, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentyloxycarbonyl, liexyloxycarbonyl, octyloxycarbonyl, nonyloxycarbonyl, decyloxycarbonyl, undecyloxycarbonyl, dodecyloxycarbonyl, methylcarbonyl, ethylcarbonyl, propylcarbonyl, butylcarbonyl, pentylcarbonyl, hexylcarbonyl, octylcarbonyl, nonylcarbonyl, decylcarbonyl, undecylcarbonyl, dodecylcarbonyl, methylcarbonyloxy, ethylcarbonyloxy, propylcarbonyloxy, butylcarbonyloxy, pentylcarbonyloxy, hexylcarbonyloxy, octylcarbonyloxy, nonylcarbonyloxv, decylcarbonyloxy, undecylcarbonyloxy, dodecylcarbonyloxy, and the like. Especially preferred groups have 1 to 12 carbon atoms and are unbranched.
By the expression C1-C20-alkenyl it should be understood to mean, in the context of this invention, alkenyl groups with 3 to 20 carbon atoms, such as 2E-alkenyl, 3Z-alkenyl, 4E-alkenyl and alkenyl with a terminal double bond, e.g. alkyl, 3-butenyl, 4-pentenyl, 5-hexenyl, 6-heptenyl, 7-octenyl, 8-nonenyl, 9-decenyl, 10-undecenyl and the like. Especially preferred are alkenyls with a terminal double bond having 3 to 12 carbon atoms.
By the expression halogen it should be understood to mean, in the context of this invention, fluorine, chlorine, bromine, iodine. Compounds containing fluorine and chlorine are particularly preferred.
Preferred compounds with formula I are compounds with formulae I-A to I-F 
wherein, one or two non-adjacent CH2 groups of the trans-1,4-cyclohexylene ring may be replaced by oxygen and one or two non-adjacent CH groups of the 1,4-phenylene ring, may be replaced by nitrogen;
L11, L12, L13 represent, independently, hydrogen, C1-C20-alkykl, C1-C20-alkenyl, C1-C20-alkoxy, C1-C20-alkoxycarbonyl, formyl, C1-C20-alkylcarbonyl, C1-C20-alkylcarbonyloxy, halogen, cyano or nitro;
Z4 represents a single bond, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OOCxe2x80x94, xe2x80x94(CH2)4xe2x80x94, xe2x80x94O(CH2)3xe2x80x94, xe2x80x94(CH2)3Oxe2x80x94 or Cxe2x89xa1Cxe2x80x94;
Z5 represents a single bond, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OOCxe2x80x94, or xe2x80x94Cxe2x89xa1Cxe2x80x94; and
S1, S2 and R have the meaning indicated in Formula I.
Compounds with the formulae I-A, I-B and I-D are especially preferred.
Of the compounds with formula I-A, particular preference is given to compounds with the formula I-A-1 and I-A-2 
wherein
L11, L12, L13 represent, independently, hydrogen, C1-C12-alkykl, C1-C12-alkenyl, C1-C12-alkoxy, C1-C12-alkoxycarbonyl, formyl, C1-C12-alkylcarbonyl, C1-C12-alkylcarbonyloxy,fluorine, chlorine, cyano or nitro;
Z4 represents xe2x80x94CH2CH2xe2x80x94, xe2x80x94OCH2, xe2x80x94COOxe2x80x94, xe2x80x94OOCxe2x80x94;
Z5 represents a single bond, xe2x80x94CH2CH2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OOCxe2x80x94, or xe2x80x94Cxe2x89xa1Cxe2x80x94;
R represents a crosslinkable groups with the structure CH2xe2x95x90CHxe2x80x94, CH2xe2x95x90CHxe2x80x94COOxe2x80x94, CH2xe2x95x90C(CH3)xe2x80x94COOxe2x80x94, CH2xe2x95x90C(Cl)xe2x80x94COOxe2x80x94, 
xe2x80x83especially CH2xe2x95x90CHxe2x80x94COOxe2x80x94;
m, n each represent, independently, a whole number from 2 to 20, especially from 2 to 12.
Of the compounds with the formula I-B, particular preference is given to compounds with formula 
wherein
L13 represents hydrogen, C1-C12-alkykl, C1-C12-alkenyl, C1-C12-alkoxy, C1-C12-alkoxycarbonyl, formyl, C1-C12-alkylcarbonyl, C1-C12-alkyl-carbonyloxy, fluorine, chlorine, cyano or nitro;
Z4 represents xe2x80x94CH2xe2x80x94CH2xe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OOCxe2x80x94; particularly xe2x80x94COOxe2x80x94;
Z5 represents a single bond, xe2x80x94CH2CH2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OOCxe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94; particularly a single bond;
R represents a crosslinkable group with the structure CH2xe2x95x90CHxe2x80x94, CH2xe2x95x90CHxe2x80x94COOxe2x80x94, CH2xe2x95x90C(CH3)xe2x80x94COOxe2x80x94, CH2xe2x95x90C(Cl)xe2x80x94COOxe2x80x94, 
xe2x80x83especially CH2xe2x95x90CHxe2x80x94COOxe2x80x94;
m, n each represent, independently, a whole number from 2 to 20, especially from 2 to 12.
Of the compounds with formula I-D, quite particular preference is given to compounds of formula I-D-1 
wherein
Z5 represents a single bond, xe2x80x94CH2CH2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OOCxe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94;
L11, L12 represent, independently, hydrogen, C1-C12-alkyl, C1-C12-alkenyl, C1-C12-alkoxy, C1-C12-alkoxy-carbonyl, formly, C1-C12-alkylcarbonyl, C1-C12-alkylcarbonyloxy, fluorine, chlorine, cyano or nitro;
R represents a crosslinkable group with the structure CH2xe2x95x90CHxe2x80x94, CH2xe2x95x90CHxe2x80x94COOxe2x80x94, CH2xe2x95x90C(CH3)xe2x80x94COOxe2x80x94, CH2C(Cl)xe2x80x94COOxe2x80x94, 
xe2x80x83especially CH2xe2x95x90CHxe2x80x94COOxe2x80x94;
m, n each represent, independently, a whole number from 2 to 20, especially from 2 to 12.
The essential structural element of the compounds with formula I is a structural unit with formulae a1 or a2 
Compounds of formula (I) having the structural element a1 or a2 may be prepared from compounds of formula (II), a 4-(trans-4-hydroxycyclohexyl)phenol. The compounds of formula (II) are also new and fall within the scope of the invention. 
wherein
X represents halogen, xe2x80x94CH2xe2x80x94CHxe2x95x90CH2, xe2x80x94OR2, xe2x80x94COOR2, xe2x80x94COR2, xe2x80x94OCOR2; and
R2 represents C1-C20-alkyl, especially C1-C12-alkyl.
The compounds according to the invention, with formula I, can be readily synthesised using known methods, such as those of Schemes 1-5. Formation of links Z1, Z2, Z3, for example, between the rings or ring systems A and B listed in formula I have been described on several occasions in the liquid crystal literature, and are well known to a person skilled in the art. A small quantity of 2,6-di-tert-butyl-4-methylphenol/xe2x80x9cbutyl hydroxytoluenexe2x80x9d (BHT) is added to each stage to prevent undesirable thermal crosslinking. 
The compounds of formula I may be used alone, in the form of mixtures with other compounds of formula I or with other liquid crystal components. Preferred liquid crystalline mixtures contain at least two components. For liquid crystalline mixtures containing additional components other than compounds of formula I, it is preferred that these additional liquid crystalline components contain a photo-crosslinkable group. One or more chiral compounds may also be contained in the mixture.
The good solubility and miscibility of the compounds with Formula I means that liquid crystal mixtures containing a high proportion of compound of Formula I may be prepared. Such mixtures may contain up to 100% by weight of the compounds of formula I.
The mixtures according to the invention preferably contain not only one or more compounds with Formula I, but also one or more compounds from the group of compounds with the general formulae 
wherein
X represents hydrogen, C1-C20-alkyl, C1-C20-alkenyl, C1-C20-alkyloxy, C1-C20-alkyloxy carbonyl, formyl, C1-C20-alkyl carbonyl, C1-C20-alkyl carbonyloxy, fluorine, chlorine, bromine, cyano or nitro;
mxe2x80x2 represents a whole number from 2 to 20;
t represents a whole number from 2 to 12;
Z represents xe2x80x94COOxe2x80x94, xe2x80x94OOCxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94O(CH2)3xe2x80x94, xe2x80x94OOC(CH2)2xe2x80x94, xe2x80x94COO(CH2)3xe2x80x94;
D represents 1,4-phenylene, trans-1,4-cyclohexylene, pyridine-2,5-diyl, pyrimidine-2,5-diyl or trans-1,4cyclohexylene-1,4-phenylene;
E 1,4phenylene, or 2- or 3-fluoro-1,4phenylene;
Sxe2x80x2 xe2x80x94(CH2)mxe2x80x94 or xe2x80x94O(CH2)mxe2x80x94;
Ra represents crosslinkable groups with the structure CH2xe2x95x90CHxe2x80x94, CH2xe2x95x90CHxe2x80x94COOxe2x80x94, CH2xe2x95x90C(CH3)xe2x80x94COOxe2x80x94, CH2xe2x95x90C(Cl)xe2x80x94COOxe2x80x94, 